Popping in speakers when playing PS2

This is a problem I've always had...I just ignored it until a few seriously good games came out that kept me glued to my PS2 for longer than 30 minutes in a sitting (Twisted Metal Black and GT3).
I'm using the optical out from the PS2 to my H/H AVR-7000. In portions of games where the sound is more active I get very annoying and harsh pops and cracks. These artifacts totally drown out the soundtrack (and effects) causing me to finish in 2nd place in every GT3 race (hell, I've got to blame my performance on something!).
Any ideas how to fix this? I'm considering dumping the optical audio out for analog.
-Camp